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9

Gravity is a fictitious force, actually, much like centrifugal force. In a free falling frame of reference it disappears. In general relativity (GR) gravity is just a result of (differential) geometry: space-time curvature. The inverse square law is just the low energy approximation, but the actual equation for gravity derived from GR is more complex than ...


8

It's hard to say much about this planet, given that most of its properties are unknown. It hasn't been directly observed; instead, its effects on Trans-Neptunian Objects (TNOs) have been simulated and match observations. That said, its mass can be estimated, which is why it is conjectured to be the core of a giant planet. One of the papers that Batygin ...


7

Space-time is not "made" of anything, it is merely a medium or coordinate system. Think about the grid lines on a map, they aren't "made" of anything, they're just a representation of the geometry of the Earth. Space-time is a concept envisaged by Einstein when he wrote his theory of Special Relativity that the properties of space and time become ...


7

Thommes et al. (2001) ran simulations and found that, at optimal conditions (namely, a planet of ~ 10 Earth masses), migration can be complete with ~ 100,000 years. Note that this was done before in-depth research was done on the Nice model, which is very similar. However, the mechanisms are different, as are the planet masses. The difference in timescales ...


6

It all depends on your frame of reference, but the biggest speeds caused by gravity will involve black holes or perhaps neutron stars. From the point of view of a far external observer, an infalling object (from infinity) reaches a maximum inward speed of $0.385c$ (where $c$ is the speed of light) towards the black hole at 3 times the Schwarzschild radius. ...


5

Short answer is yes. The only way radiation pressure would be a factor was if the ball was in orbit around the Sun, this would mean that the slight pressure it feels would cause it to drift away slowly (assuming its made of the most heat resistant material on Earth!). But in your question you said "placed" near the sun not in orbit around it, so the strength ...


4

The answer depends on the size and mass of the ball. It also depends on its ability to reflect light (albedo $A$), but let's forget that for a moment. Pressure vs. gravity Solar pressure decreases with $R^2$ (the inverse square law). At Earth, which is located at a distance of $1\,\mathrm{AU}$ from the Sun, we receive an irradiance $S_0 = ...


4

As a hobbyist, I'll give a limited answer. Gravitational force is particle or wave? Until we actually find out what gravity is, the safe answer here is that we don't know, but it's probably a wave and a particle. Most (perhaps all) fundamental particles in quantum physics are waves and particles. Light for example, Electrons too, though we might ...


4

There may be Sednoids there. Sednoids are a hypothetical class of "inner Oort Cloud objects" named after their prototype, Sedna. Sedna's aphelion is ~936 AU, bringing it close to the inner boundary of the Oort Cloud. Sednoids may have aphelions ranging from about 100 AU to 1,000 AU. The problem is, only two Sednoids have beet detected to date, 90377 Sedna ...


3

For a lot of my uninformed life, I have doubted the existence of gravitons or even that gravity is an actual "force" (like electromagnetism). Gravity is a force like electromagnetism, but it does have a special property in that all test particles fall the same way in a gravitational field, no matter their composition. This means that inertial masses and ...


3

First, the fact that gravity falls off $1/r^2$ is visible in the metric. The metric describes the curvature of the space. For space around a massive object this is the Schwarzchild metric $$ ds^2 = -\left(1-\frac{r_s}{r}\right)dt^2 + \left(1-\frac{r_s}{r}\right)^{-1}dr^2 + r^2(d\theta^2 + \sin^2\theta d\phi^2) $$ Clearly, if $r>>r_s$ this looks like ...


3

I think the wikipedia page gives a reasonable overview of why gravitational waves give us a window on the universe that is either not observable or is complementary to the view we get from electromagnetic waves (or neutrinos). But let's have a specific example. The potential of LIGO (and as I'm writing this, no discovery has been confirmed or announced) is ...


3

Since the collision is perfectly elastic, the ball's velocity goes from -80 km/h from the train's reference point (negative being towards the train) to +80 km/h from the train's reference point, a speed increase of 160 km/h. For a stationery observer, therefore, the velocity goes from -30 km/h (towards the train) to 130 km/h, an increase of 160 km/h. ...


2

General relativity can be used to discuss, theoretically, what happens to objects as they approach the event horizon of a black hole; it all has to do with your point of view. Outside viewers, those not affected by the gravity of the black hole, would view an object approach the event horizon slowly and pretty much never enter past the horizon. For the ...


2

A quick search up on google you would find this: Gravity causes every object to pull every other object toward it. Some people think that there is no gravity in space. In fact, a small amount of gravity can be found everywhere in space. Gravity is what holds the moon in orbit around Earth. Why is this? That's because: Outer space is the ...


2

General relativity is often explained as saying spacetime is curved by gravity, what does this mean? It means that general relativity can be formulated in a way in which its mathematics have a very direct analogue to differential geometry on a curved four-dimensional manifold. In other words, the way test particles would behave under the influence of ...


2

There is no fully satisfactory quantum theory of gravity. The electromagnetic field is quantized, the quantum excitations are photons. It would be reasonable to believe that the gravitational field would also be quantised, and the quanta would be particles, called gravitons. However there is neither a theoretical, nor an experimental basis for the existence ...


2

Ignoring details such as the oblateness of the Earth, atmospheric drag, third body influences such as the Moon and the Sun, relativity, ..., the period of a satellite of negligible mass (even the International Space Station qualifies as a "satellite of negligible mass") is $T=2\pi\sqrt{\frac {a^3}{\mu_\mathrm{Earth}}}$. Neither Newton's gravitational ...


1

Think at the surface of a ball. A straight line within this curved surface is a great circle. Take some point on the ball. Draw two great circles (apparent straight lines in the surface) starting in this point, with some non-zero initial angle. The two apparent straight lines intersect at the opposite side of the ball. Wrongly assuming the surface of the ...


1

$\mu$ is a quantity that can be easily observed (semi-) directly. It can be easily derived from orbital period of orbiting bodies or acceleration of falling bodies, even if their mass is significantly smaller than the mass of the body you're measuring $\mu$ for. Now the only way to really obtain G is to divide $\mu$ by mass of your celestial body. And ...


1

In the intergalactic medium — the most dilute regions of the Universe between the galaxies — as CipherBot writes you'll find roughly one hydrogen per cubic meter, i.e. the density is $\sim10^{-6}\,\mathrm{atoms}\,\mathrm{cm}^{-3}$, or $\sim10^{-30}\,\mathrm{g}\,\mathrm{cm}^{-3}$, or, in terms of energy (since mass and energy are equivalent through $E=mc^2$), ...


1

The Kuiper belt and the Scattered disk are widely believed to lie in the space between the outer planets and the Oort cloud, but not to reach all the way out to the Oort cloud (apparently due to resonances with Neptune and a scarcity of sighted object much outside the 1:2 resonance orbit). The various dwarf planets of the outer solar system are sometimes ...


1

What is the maximum speed that can be achieved because of acceleration due to gravity? The speed of light. But there's a catch. In other words which is the strongest and largest gravitational field discovered in the universe till date. That of a black hole. Sagittarius A* is thought to be the location of a supermassive black hole. What is ...



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